Spontaneous Rupture and Thrombotic Effects in a Swine Model of Untreated Abdominal Aortic Aneurysms

Background: In our previous canine model of abdominal aortic aneurysm, although aneurysm growth was observed, the aneurysms did not rupture. This prompted us to develop a swine model, which has the advantage of fibrinolytic and coagulation systems similar to those found in humans. Methods: We simulated aneurysms by connecting fascia pouches to the aorta. In nine pigs, two pieces of fascia (5 x 8 cm each) were sutured to the posterior surface of the aorta. After the lateral edges of the aorta were sutured together, the aorta was clamped below the renal arteries and at the aortic bifurcation. We then resected a piece of aorta within the pouch, clamped the pouch below the open roof, and unclamped the aorta. When the entire pouch had been sutured, the last clamp was removed and blood flowed into the "aneurysm." The total aortic cross clamp time was between 4 and 25 minutes. Results: "Aneurysm" size ranged from 3.0 x 2.5 cm to 7.5 x 4.0 cm (length x width). Aneury sm rupture occurred in seven pigs between 4 and 43 days after initial surgery; however, rupture never occurred at a suture site. Aneurysm size at rupture was two to four times greater than that of the original pouch. We found thrombus in all of the aneurysms examined more than 2 days after surgery. Histology revealed aneurysm walls that were thicker than the fascia. Although fascia segments could be identified because of their characteristic trilayer of thick collagen fibers, most of the aneurysm wall contained thin collagen fibers. These observations are consistent with new collagen production. Conclusion: We constructed a swine model of abdominal aortic aneurysm that possessed the features of growth and rupture necessary to simulate human aneurysms. Our method will allow techniques designed to isolate aneurysms from the circulation to be tested in a model with a fibrinolytic system similar to that of humans.